The invention relates to a cylinder head gasket wherein a surface pressure on a peripheral bead and a surface pressure on a sealing bead for a water or oil hole can be optimized.
A cylinder head gasket formed of a single metal plate or a plurality of metal plates includes a peripheral bead at a position corresponding to a periphery of a cylinder head or head block of a cylinder. The peripheral bead suppresses bending of a periphery of the head block when the head block of the cylinder is tightened against a cylinder block. Or, the peripheral bead suppresses looseness of tightened bolts, and further, is provided to secondarily seal a fluid hole, such as a water hole and an oil hole, which is provided with an independent sealing bead therearound.
However, in the request for light weight of the engine, in case a peripheral bead is formed to have the same height and width as those of the sealing bead disposed around the fluid hole, when the head block is tightened against the cylinder block by the bolts with a suitable tightening force, a bending may occur on the periphery of the head block.
In view of the above problem, the present invention has been made and an object of the invention is to provide a cylinder head gasket, wherein when the head block is tightened by bolts against the cylinder block, substantially uniform and optimum load can be obtained on a peripheral bead of the cylinder head gasket.
Another object of the invention is to provide a cylinder head gasket, wherein the surface pressures of a sealing bead for a fluid hole and a peripheral bead can be optimized.
Further objects and advantages of the invention will be apparent from the following description of the invention.
In order to attain the above objects, a cylinder head gasket according to the present invention is structured such that a height of a peripheral bead disposed on a metal plate constituting the gasket is entirely or partially made lower than that of a sealing bead for a fluid hole.
According to a preferable embodiment of the present invention, the height of the peripheral bead in a portion where the peripheral bead is made low, is in a range of one third to two thirds relative to the height of the sealing bead for the fluid hole.
Also, in the cylinder head gasket according to the present invention, a width of the peripheral bead formed on a metal plate constituting the gasket can be entirely or partially made wider than that of the sealing bead for the fluid hole.
In the cylinder head gasket having the structure as described above, when the gasket is manufactured, the height of the peripheral bead is formed lower than that of the liquid hole sealing bead, preferably, the height is set to about half of the height of the sealing bead for the fluid hole, or the width of the peripheral bead is entirely or partially formed wider than that of the sealing bead for the fluid hole. When tightened by the bolts, both beads are compressed to a specific height between the cylinder block and the cylinder head, or both beads are compressed under the state where the cylinder head is bent within a tolerance, so that the optimum load share can be obtained at the time of compression of the sealing bead for the fluid hole and the peripheral bead. Also, substantially uniform or appropriate surface pressure can be obtained at the peripheral bead.